THE  UNIVERSITY 
OF  ILLINOIS 


cop.  "2. 


AfiRIGULTURAL 
UUUBY 


ING 


\ 


BULLETIN  No.  230 


ELIMINATION  OF  GERMS  FROM  DAIRY 

UTENSILS 

I.  BY  RINSING      II.  BY  DRYING  IN  SUN  AND  AIR 
BY  M.  J.  PRUCHA  AND  H.  A.  HARDING 


URBANA,  ILLINOIS,  NOVEMBER,  1920 


CONTENTS  OF  BULLETIN  No.  230 

PACK 

INTRODUCTION    139 

METHODS  OF  STUDY 140 

How  the  Utensils  Were  Washed 140 

Method  of  Counting  Bacteria  in  the  Utensils 141 

EXPERIMENTAL  DATA: 

PART  I.  ELIMINATION  OF  GERMS  FROM  CANS  BY  EINSING  WITH  HOT  WATER.  .142 

Cooling  Effect  of  Cans  on  Rinse  Water 143 

Effect  of  Einse  Water  on  Germ  Life  in  Cans 144 

PART  II.    ELIMINATION  OF  GERMS  PROM  CANS  BY  DRYING  IN  SUN  AND  AIR..  157 
General  Condition  of  the  Cans  and  Pails  After  Being  Kept  on  the  Eack.  .157 

Number  of  Bacteria  in  Untreated  Cans 163 

Bacteria  in  Cans  and  Pails  After  Eight  Hours  of  Exposure  to  Sun  and  Air .  163 

Bacteria  in  Cans  After  Twenty  Hours '  Exposure  to  Sun  and  Air 164 

Bacteria  in  Dry  Cans  and  in  Moist  Cans 165 

Importance  of  Dryness  in  Controlling  Germ  Life  in  Utensils 167 

GENERAL  DISCUSSION  .  . .  168 


ELIMINATION  OF  GERMS  FROM  DAIRY 

UTENSILS 

I.  BY  RINSING     II.  BY  DRYING  IN  SUN  AND  AIR 

Br  M.  J.  PRUCHA,  CHIEF  IN  DAIRY  BACTERIOLOGY  AND  . 
H.  A.  HARDING,  CHIEF  IN  DAIRY  BACTERIOLOGY 

INTRODUCTION 

Before  saying  that  a  milk  is  good  one  wishes  to  know  that  it  is 
rich,  safe,  clean,  and  sweet.  Accordingly,  quality  in  milk  is  said  to 
depend  upon  the  four  items:  (1)  food  value,  (2)  healthfulness, 
(3)  cleanliness,  and  (4)  keeping  quality.1 

Of  these  four  elements,  keeping  quality,  or  the  ability  to  remain 
sweet,  is  the  most  difficult  to  protect  successfully  during  the  produc- 
tion and  delivery  of  the  milk.  If  it  were  not  for  the  action  of  germ 
life  on  the  milk  it  would  remain  sweet  indefinitely.  However,  every 
time  milk  is  exposed  to  dust  or  is  changed  from  one  container  to  an- 
other it  receives  germ  life.  This  germ  life  living  and  growing  in  the 
milk  breaks  the  milk  sugar  into  acid  and  sours  the  milk.  Accordingly 
the  first  step  in  protecting  the  keeping  quality  of  milk  is  to  reduce  as 
much  as  practicable  the  number  of  germs  which  get  into  it. 

In  Bulletin  204  of  this  station2  it  was  pointed  out  that  the  uten- 
sils in  which  milk  is  handled  are  an  extremely  important  source  of 
germ  life;  hence,  it  is  good  dairy  practice  to  reduce  as  far  as  prac- 
ticable the  number  of  utensils  coming  into  contact  with  the  milk.  As 
there  is  a  limit  to  such  reduction  it  is  also  important  to  know  how 
the  necessary  utensils  may  be  handled  so  as  to  add  the  smallest  num- 
ber of  germs  to  the  milk. 

As  a  part  of  the  washing  process,  dairy  utensils  are  practically 
always  rinsed,  hot  water  being  commonly  used  for  this  purpose.  This 
rinsing,  in  addition  to  removing  traces  of  the  washing  powder,  me- 
chanically removes  some  of  the  remaining  germ  life  and  if  the  water 
is  hot  enough  it  also  destroys  some  of  the  germs.  A  study  of  the 
effect  of  rinsing  with  water  upon  the  germ  life  in  the  cans,  is  reported 
in  Part  I  of  this  bulletin.  This  study  was  confined  to  cans  because 

Warding,  H.  A.,  Breed,  E.  S.,  Stocking,  W.  A.,  Jr.,  and  Hasting,  E.  G., 
What  is  Meant  by  "Quality"  in  Milk.  111.  Agr.  Exp.  Sta.  Circ.  205.  1917. 

Trucha,  M.  J.,  Weeter,  H.  M.,  and  Chambers,  W.  H.,  Germ  Content  of  Milk: 
II  As  Influenced  by  the  Utensils.  111.  Agr.  Exp.  Sta.  Bui.  204.  1918. 

139 


140  BULLETIN  No.  230  [November, 

among  the  common  dairy  utensils  cans1  are  the  outstanding  factor  in 
adding  germ  life  to  the  milk. 

Perhaps  the  simplest  and  most  universal  treatment  given  utensils 
is,  after  washing,  to  invert  them  to  dry  on  a  rack,  preferably  in  the 
sun.  The  effect  of  this  drying  in  the  air,  upon  the  germ  life  in  cans 
and  pails,  has  been  studied  and  the  results  are  given  in  Part  II  of 
this  bulletin. 

In  stating  the  amount  of  germ  life  in  milk  it  is  customary  to  give 
the  number  present  in  a  cubic  centimeter  (about  20  drops),  or  more 
briefly  "per  cc."  The  public  has  become  familiar  with  the  fact  that 
certified  milk  ordinarily  contains  less  than  10,000  bacteria  per  cc. 
and  that  the  presence  of  1,000,000  bacteria  per  cc.  indicates  that  the 
keeping  quality  of  the  milk  has  been  seriously  impaired.  Accord- 
ingly it  has  seemed  helpful  to  state  the  germ  life  which  would  be 
contributed  by  any  given  utensil  in  terms  of  the  number  of  germs 
per  cc.  it  would  add  if  filled  with  sterile  milk.  It  is  believed  that 
this  form  of  expressing  the  results  will  not  only  assist  in  comparing 
the  results  of  handling  utensils  in  different  ways,  but  it  will  also  in- 
dicate whether  the  contamination  arising  from  any  particular  uten- 
sil is  heavy  enough  to  furnish  any  considerable  part  of  the  final  germ 
content  of  the  milk. 

It  is  a  regrettable  fact  that,  particularly  in  hot  weather,  much  of 
the  milk  as  it  is  delivered  at  the  shipping  station  or  the  bottling  plant 
is  heavily  seeded  with  germ  life.  In  the  hope  of  finding  practicable 
means  by  which  this  seeding  could  be  reduced,  the  present  studies 
were  directed  primarily  to  operations  which  could  be  carried  out  on 
the  farm,  tho  the  results  are  equally  applicable  in  other  places. 

The  larger  part  of  the  data  reported  in  this  bulletin  was  obtained 
during  1915-1917.  Messrs.  H.  M.  Weeter  and  W.  H.  Chambers,  then 
members  of  this  department,  took  an  active  part  not  only  in  the  rou- 
tine conduct  of  experiments  but  also  in  developing  the  plans  for  this 
study.  The  faithful  service  and  intelligent  interest  in  the  earlier  por- 
tions of  these  studies  of  both  of  these  men  is  gratefully  acknowledged. 

METHODS  OF  STUDY 

These  studies  were  made  upon  the  eight-gallon  cans  and  the  four- 
teen-quart  covered  milking  pails  used  in  caring  for  the  milk  from  the 
University  dairy  herds.  The  handling  of  these  pails  and  cans  was  in 
close  accord  with  good  commercial  practice. 

How  THE  UTENSILS  WERE  WASHED 

The  cans  were  washed  at  the  University  creamery  in  a  vat  contain- 
ing about  40  gallons  of  water  at  about  110°  F.  to  which  was  added 

'See  pages  222-230  and  246-247  of  Bui.  204,  HI.  Agr.  Exp.  Sta.,  noted  on 
preceding  page. 


ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS  141 

one  percent  sodium-carbonate  washing  powder.  Each  can  was  scrubbed 
with  a  brush,  and  after  draining  for  about  five  seconds  was  rinsed  in 
another  vat  containing  plain  water  at  about  110°  to  120°  F.  The  pails 
were  washed  in  a  similar  manner  except  that  the  washing  took  place 
at  the  farm. 

METHOD  OF  COUNTING  BACTERIA  IN  THE  UTENSILS 

After  the  utensils  had  received  the  desired  treatment,  one  liter 
(approximately  one  quart)  of  sterile  cool  water  was  poured  into  each 
can  or  pail,  and  after  a  thoro  shaking  the  water  was  poured  out  and 
the  number  of  bacteria  removed  by  this  water  taken  as  the  number 
present  in  the  utensil.  The  extended  tests  of  this  method  of  determi- 
nation which  are  reported  in  Bulletin  204  (pages  222-226)  indicate 
that  the  numbers  of  bacteria  found  in  this  way  represent  about  75 
percent  of  the  total  which  would  be  obtained  by  repeated  rinsings. 
This  method  of  testing  was  employed,  not  because  it  was  considered 
ideal,  but  because  it  seemed  the  best  available  method. 

The  plate  method  was  used  for  counting  the  bacteria  in  this  water. 
In  all  cases  three  plates  were  prepared  from  each  of  two  dilutions. 
The  counts  recorded  in  this  bulletin  are  in  each  case  the  average  of 
the  counts  of  the  three  plates  from  the  dilution  in  which  the  number 
of  colonies  approached  the  closer  to  200  per  plate. 

All  the  plates  were  incubated  for  five  days  at  20°  C.  and  for  two 
days  at  37°  C.  before  they  were  counted. 

Nutrient  agar  of  the  following  composition  was  used  for  plating: 

Agar  shreds 15  grams 

Liebig  's  meat  extract 3  grams 

Witte  's  peptone 10  grams 

Lactose  10  grams 

Distilled  water  1  liter 

The  resulting  medium  had  a  reaction  varying  between  6  cc.  and 
9  cc.  normal  acid  to  the  liter,  phenolphthalein  being  used  as  an 
indicator. 


142  BULLETIN  No.  230  [November, 

EXPERIMENTAL  DATA 

PART  I.    ELIMINATION  OF  GERMS  FROM  CANS  BY  RINSING 
WITH  HOT  WATER 

The  rinsing  of  utensils  is  commonly  employed  to  complete  the 
cleaning  process  and  to  remove  traces  of  washing  powder.  The  pres- 
ent study  is  concerned  primarily  with  the  effect  of  rinsing  upon  the 
germ  life  in  the  utensils. 

According  to  common  commercial  practices  in  moderate  sized 
plants,  cans  as  they  come  from  the  washing  vat  are  rinsed  in  a  vat 
of  warm  water.  This  warm  water  is  so  efficient  in  removing  germs 
from  the  cans  that  the  vat  of  rinse  water  quickly  becomes  loaded  with 
germ  life.  Samples  of  typical  rinse  water  were  employed  on  three 
different  days  in  seeding  the  cans  reported  upon  in  Table  6,  and  these 
samples  carried  4,220,000,  7,650,000,  and  11,500,000  bacteria  per  cc. 
respectively.  In  considering  the  germ  content  of  cans  rinsed  under 
these  conditions  it  should  be  remembered  that  about  10  cc.  of  this 
rinse  water  adheres  to  the  inside  of  even  well-drained  cans. 

The  present  study  is  concerned  primarily  with  conditions  as  they 
exist  on  farms,  and  here  the  rinse  water  commonly  comes  into  con- 
tact with  one  or  at  most  only  a  few  utensils.  The  tests  here  described 
were  made  during  June,  July,  and  October,  1915,  and  April,  May, 
and  June,  1916.  In  these  experiments  80  cans  were  rinsed  with  water 
at  70°  F.,  103  were  rinsed  with  water  at  150°  F.,  and  266  were  rinsed 
with  water  at  about  205°  F.,  making  a  total  of  449  cans  examined. 

The  cans  which  were  to  be  studied  were  first  washed,  and  after 
standing  in  the  creamery  from  one  to  four  hours  were  rinsed  in 
the  following  manner :  A  measured  amount  of  rinse  water  was  poured 
slowly  into  each  can  in  such  a  way  that  the  stream  of  water  came  into 
contact  first  with  the  upper  edge  of  the  neck  of  the  can  and  then  ran 
down  the  inner  surface.  A  portion  of  the  water  was  also  poured  over 
that  part  of  the  lid  which  comes  in  contact  with  the  milk,  and  this 
water  was  also  allowed  to  run  into  the  can.  The  cover  was  replaced 
and  the  can  was  then  shaken  for  30  seconds  in  order  that  the  inner 
surface  of  the  can  might  come  in  contact  with  the  rinse  water.  After 
this  the  water  was  poured  from  the  can. 

The  effectiveness  of  hot  water  was  tested  at  two  temperatures — 
at  150°  F.  and  at  about  205°  F.  At  each  temperature  different 
amounts  of  water  were  tested:  at  150°  F.,  1  quart,  iy2  quarts, 
2  quarts,  and  4  quarts ;  and  at  205°  F.,  1  quart,  iy2  quarts,  2,  3,  4,  6, 
and  9  quarts. 

Rinse  water  at  70°  F.  was  tested  on  the  same  days  that  similar  cans 
were  rinsed  with  hot  water,  the  only  difference  in  the  treatment  of 
the  cans  being  in  the  temperature  of  the  water  used. 


19*0] 


ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS 


143 


It  will  be  noted  that  the  application  of  this  water  to  the  cans  con- 
stituted in  reality  a  second  rinsing  inasmuch  as  the  cans  had  been 
rinsed  in  connection  with  the  regular  washing  process.  However, 
in  view  of  the  high  germ  content  of  the  wash  water  employed  in  con- 
nection with  the  regular  washing  process  and  the  great  variability  of 
the  germ  content  of  ordinary  cans,  it  is  thought  that  using  cans 
washed  in  the  regular  way  gave  more  uniform  material  upon  which 
to  test  the  effects  of  the  hot-water  treatment. 

COOLING  EFFECT  OF  CANS  ON  RINSE  WATER 

Everyone  knows  that  when  cold  hands  are  placed  in  hot  water  the 
hands  are  warmed  and  the  water  cooled.  Likewise  everyone  under- 
stands that  when  a  cool  can  is  rinsed  with  hot  water  the  can  is  warmed 
and  the  water  cooled  tho  few  realize  the  extent  of  this  temperature 
change. 

The  decrease  in  the  temperature  of  the  various  amounts  of  rinse 
water  used  in  these  studies  was  determined  by  taking  the  temperature 
of  the  water  just  before  it  was  poured  into  the  can  at  72°  F.  and  again 
immediately  after  it  was  poured  out,  an  interval  of  about  sixty  seconds. 

The  observations  made  upon  the  reduction  in  temperature  of  the 
rinse  water  as  used  in  these  studies  are  summarized  in  Tables  1  and  2. 

TABLE  1. — EFFECT  OF  CANS  IN  REDUCING  TEMPERATURE  OF  RINSE  WATER 
When  the  cans  were  treated  singly 


Amount  of 
water 

Temperature  of  water  — 

Drop  in 
temperature 

Before  rinsing 

After  rinsing 

quarts 

°F. 

•F, 

°F. 

1 

150 

110 

40 

2 

150 

122 

28 

4 

150 

131 

19 

1 

210 

140 

70 

2 

210 

154 

56 

4 

210 

170 

40 

6 

210 

180 

30 

9 

210 

187 

23 

TABLE  2. — EFFECT  OF  CANS  ON  TEMPERATURE  OF  RINSE  WATER 
When  four  cans  were  rinsed  in  succession  by  the  same  lot  of  rinse  water 


Amount  of 
water 

Before 
rinsing 

Temperature  of  water  — 

Total  drop 
in 
temperature 

After 
1st  can 

After 
2d  can 

After 
3d  can 

After 
4th  can 

quarts 
2 
6 

Of, 

210 
210 

°F. 
158 
178 

°F. 
131 
160 

°F. 

113 
150 

°F. 
100 
138 

°F. 
110 

72 

As  shown  in  Table  1,  the  decrease  in  the  temperature  of  the  hot 
water  during  the  process  of  scalding  was  very  marked  and  depended 
both  on  the  amount  of  water  used  and  on  its  initial  temperature.  For 
example,  one  quart  of  water  at  150°  fell  in  temperature  to  110°,  a  drop 


144  BULLETIN  No.  230  [November, 

of  40  degrees;  while  four  quarts  decreased  to  131°,  a  drop  of  19  de- 
grees. When  the  cans  were  scalded  with  water  at  210°,  one  quart  of 
water  decreased  in  temperature  from  210°  to  140°,  and  four  quarts 
dropped  to  170°,  a  loss  of  70  and  40  degrees  respectively. 

The  results  in  Table  2  show  that  when  six  quarts  of  boiling  water 
was  applied  successively  to  four  cans  at  72°  F.  the  temperature  of  the 
water  fell  from  210°  to  138°,  a  drop  of  72  degrees,  while  after  a  simi- 
lar application  of  two  quarts  of  boiling  water  the  temperature  of  the 
water  fell  to  100°  F.,  which  is  a  drop  of  110  degrees. 

It  is  thus  seen  that  when  hot  water  is  poured  into  utensils  for  the 
purpose  of  scalding  them  the  heat  passes  quickly  from  the  water  to  the 
walls  of  the  utensils. 

In  considering  the  temperatures  found  in  the  rinse  water  as  it  came 
from  the  cans  it  should  be  remembered  that  hot  water  below  140°  F. 
has  but  little  killing  effect  when  the  time  of  exposure  to  it  is  short.1 
Accordingly  rinse  water  at  150°  F.,  in  the  quantities  which  are  avail- 
able on  any  ordinary  farm,  will  be  so  promptly  cooled  as  to  have  little 
killing  effect  upon  the  germ  life  in  the  utensils.  Even  boiling  water  is 
so  promptly  cooled  by  the  cans  that  unless  two  or  more  quarts  are 
applied  directly  to  each  can  the  germ-killing  effect  is  much  less  than 
is  commonly  believed. 

That  the  cooling  effect  of  the  utensils  on  the  scalding  water  is  prob- 
ably not  fully  appreciated  by  many  dairy  operators,  is  shown  by  the 
following  observation  made  in  a  large  city  milk  plant.  It  was  the 
custom  at  this  plant  to  treat  the  pasteurizing  vat,  50  feet  of  sanitary 
pipe,  the  tubular  cooler,  and  the  tank  under  the  cooler,  with  hot  water 
for  the  purpose  of  "sterilizing"  these  utensils.  Three  hundred  gal- 
lons of  boiling  water  were  pumped  from  the  vats  thru  the  pipe,  and 
were  allowed  to  trickle  down  over  the  cooler  into  the  tank.  It  took 
about  twenty  minutes  to  pump  this  water.  When  all  of  the  water  had 
reached  the  tank  the  temperature  of  the  water  had  fallen  from  210° 
to  120°  F.,  a  drop  of  90  degrees.  Long  before  this  water  had  reached 
the  end  of  its  appointed  journey  its  temperature  had  fallen  below 
the  point  where  it  would  be  destructive  to  germ  life,  and  any  further 
reduction  of  germ  life  resulting  from  its  use  depended  solely  upon 
its  mechanical  removal  of  germs  from  the  utensils. 

EFFECT  OF  RINSE  WATER  ON  GERM  LIFE  IN  CANS 

Cans  at  the  farm  are  scalded  or  rinsed  as  a  final  step  in  removing 
the  germ  life  and  preparing  the  cans  for  receiving  milk.  Accordingly 
the  amount  of  germ  life  remaining  in  the  cans  after  such  treatment 

aSmith,  Theobald.  The  Thermal  Death-point  of  Tubercle  Bacilli  in  Milk  and 
Other  Fluids.  Jour.  Exp.  Med.  4:217-233.  1899. 

Russell,  H.  L.  and  Hasting,  E.  G.  Thermal  Death-point  of  Tubercle  Bacilli 
under  Commercial  Conditions.  Wis.  Agr.  Exp.  Sta.  Ann.  Ept.  17(1900)  :147- 
170.  1900. 


ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS  145 

is  a  matter  of  first  importance.  In  this  study  such  a  determination 
was  made  in  the  case  of  each  of  the  449  cans  tested. 

As  the  available  supply  of  hot  water  for  rinsing  utensils  at  the 
farm  is  limited,  the  question  of  how  much  rinse  water  per  can  is  really 
needed  is  likewise  important.  In  these  studies  the  use  of  varying 
amounts  of  water  was  tested,  the  range  of  these  tests  being  especially 
wide  in  the  case  of  boiling  water. 

In  the  application  of  rinse  water  to  milk  cans,  the  object  usually 
in  mind  is  the  destruction  of  germ  life.  While  such  destruction  is  a 
natural  result,  particularly  where  boiling  water  is  used,  the  rapid 
accumulation  of  germ  life  in  rinsing  vats  makes  it  evident  that  the 
mechanical  removal  of  germ  life  is  also  an  important  function  of  rinse 
water.  As  a  means  of  getting  information  regarding  the  importance 
of  this  mechanical  removal  of  germ  life  from  cans  by  rinse  water,  the 
number  of  living  germs  in  the  rinse  water  as  it  came  from  the  cans 
was  also  determined. 

The  results  of  these  studies  in  connection  with  the  rinsing  of  449 
cans  are  given  in  Table  3,  in  which  the  successive  columns  show  the 
number  of  the  can,  the  number  of  living  germs  found  in  the  rinse 
water  from  the  can,  the  number  of  living  germs  recovered  from  the 
rinsed  can  according  to  the  method  given  on  page  141,  and  the  num- 
ber of  germs  per  cubic  centimeter  which  the  can  would  have  con- 
tributed if  it  had  been  filled  with  milk. 

As  is  ordinarily  the  case  in  studies  of  germ  life  in  cans  the  results 
given  in  Table  3  show  wide  variations  in  the  findings  from  appar- 
ently similar  cans.  In  order  to  bring  this  large  amount  of  data  to- 
gether so  that  they  may  be  more  readily  compared  the  results  obtained 
from  each  group  of  cans  treated  alike  have  been  averaged.  However, 
in  considering  these  averages  the  varying  number  of  cans  which  they 
include  and  the  wide  variations  in  the  data  which  they  represent 
should  be  kept  in  mind  constantly.  . 

The  average  number  of  living  germs  removed  by  each  different 
amount  of  rinse  water  at  each  temperature  and  the  corresponding  av- 
erage number  of  germs  found  in  the  rinsed  cans  are  given  in  Table  4. 

Bacteriological  Condition  of  Cans  Rinsed  with  Water  at  70°  F. 

The  results  as  given  opposite  this  temperature  in  Table  4  show 
marked  irregularities.  By  referring  to  the  number  of  cans  in  each 
group  it  is  seen  that  a  comparatively  small  number  of  cans  are  rep- 
resented in  each  of  the  averages  except  those  where  1.5  and  6  quarts 
of  water  were  used. 

Taking  the  averages  as  a  whole,  but  remembering  that  those  rep- 
resenting cans  rinsed  with  1.5  and  6  quarts  of  water  are  the  more 
representative,  it  appears  that  cans  rinsed  with  water  at  70°  F.  and 
immediately  filled  with  milk  will  ordinarily  add  to  such  milk  about 


146 


BULLETIN  No.  230 


[November, 


10,000  bacteria  per  cc.    The  use  of  large  volumes  of  rinse  water  some- 
what reduces  the  number  of  bacteria  remaining  in  the  cans. 


TABLE  3. — EFFECT  OF  VARYING  AMOUNTS  AND  TEMPERATURES  OF  RINSE  WATER 
ON  GERM  LIFE  IN  CANS 


No.  of 
can 

Number  of  germs 
removed  by  rinse 
water 

Number  of  germs 
remaining  in  can 
after  rinsing 

Germs  per  cc.  of 
milk  due  to  can 

Cans  Rinsed  with  1  Quart  of  Water  at  70°  F. 


1 

8  000  000 

263.2 

2 

46  300  000 

1  523.2 

3 

88  000  000 

2  894.7 

4 

1  210  000  000 

39  802.6 

5 

4  630  000  000 

152  315.8 

Cans  Rinsed  with  1^  Quarts  of  Water  at  70°  F. 


6 

17  498  000 

530  000 

17.4 

7 

17  332  000 

547  000 

17.9 

8 

15  393  000 

680  000 

22.4 

9 

16  950  000 

812  000 

26.7 

10 

22  125  000 

1  102  000 

36.2 

11 

64  950  000 

1  500  000 

49.3 

12 

64  837  000 

1  550  000 

50.9 

13 

53  325  000 

2  412  000 

79.3 

14 

54  937  000 

2  467  000 

81.2 

15 

41  040  000 

3  370  000 

110.8 

16 

242  775  000 

11  320  000 

372.4 

17 

42  562  000 

12  075  000 

397.2 

18 

88  275  000 

19  500  000 

641.4 

19 

178  350  000 

30  000  000 

986.8 

20 

330  000  000 

33  500  000 

1  101.9 

21 

637  500  000 

122  000  000 

4  013.3 

22 

720  000  000 

308  600  000 

10  151.3 

23 

9  675  000  000 

810  000  000 

26  644.7 

24 

13  950  000  000 

1  877  000  000 

61  743.4 

25 

21  750  000  000  : 

3  150  000  000 

103  618.4 

Cans  Rinsed  with  3  Quarts  of  Water  at  70°  F. 


26 

35  175  000 

3  130  000 

103.0 

27 

85  200  000 

11  125  000 

366.0 

28 

154  200  000 

30  775  000 

1  012.3 

Cans  Rinsed  with  3  Quarts  of  Water  at  70°  F. 


29 

1  282  000  000 

57  700  000 

1  898.0 

30 

130  500  000 

58  750  000 

1  932.6 

31 

110  400  000 

60  200  000 

1  980.3 

32 

2  550  000  000 

213  000  000 

7  006.6 

33 

4  212  000  000 

317  000  000 

10  427.6 

34 

4  545  000  000 

362  000  000 

11  907.9 

35 

5  625  000  000 

370  000  000 

12  171.0 

36 

5  175  000  000 

485  000  000 

15  953.9 

37 

8  062  500  000 

1  120  000  000 

36  842.1 

ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS 


147 


TABLE   3. — Continued.    EFFECT  OF  VARYING  AMOUNTS   AND  TEMPERATURES  OF 
RINSE  WATER  ON  GERM  LIFE  IN  CANS 

Cans  Rinsed  with  6  Quarts  of  Water  at  70°  F. 


No.  of 
can 

Number  of  germs 
removed  by  rinse 
water 

No.  of 

can 

Number  of  germs 
removed  by  rinse 
water 

No.  of 
can  • 

Number  of  germs 
removed  by  rinse 
water 

38 

606  000 

50 

48  900  000 

62 

132  450  000 

39 

606  000 

51 

50  700  000 

63 

183  600  000 

40 

906  000 

52 

54  900  000 

64 

371  700  000 

41 

1  212  000 

53 

59  400  000 

65 

456  498  000 

42 

6  900  000 

54 

62  400  000 

66 

535  398  000 

43 

7  800  000 

55 

66  450  000 

67 

614  196  000 

44 

18  300  000 

56 

72  750  000 

68 

922  200  000 

45 

30  450  000 

57 

83  550  000 

69 

1  794  396  000 

46 

31  998  000 

58 

84  600  000 

70 

2  059  500  000 

47 

42  900  000 

59 

84  600  000 

71 

10  722  000  000 

48 

43  350  000 

60 

87  600  000 

72 

32  580  000  000 

49 

45  150  000 

61 

119  100  000 

No.  of 
can 

Number  of  germs 
removed  by  rinse 
water 

Number  of  germs 
remaining  in  can 
after  rinsing 

Germs  per  cc.  of 
milk  due  to  can 

Four  Cans  Rinsed  in  Succession  by  Same  Lot  of  9  Quarts  of  Water  at  70°  F. 


73 

549  000  000 

150  000  000 

4  934.2 

74 

1  395  000  000 

170  000  000 

5  592.1 

75 

1  350  000  000 

23  500  000 

773.0 

76 

1  530  000  000 

6  270  000 

206.2 

77 

15  300  000  000 

1  050  000  000 

34  539.5 

78 

16  200  000  000 

415  000  000 

13  651.3 

79 

25  200  000  000 

910  000  000 

29  934.2 

80 

46  800  000  000 

1  000  000  000 

32  894.7 

Cans  Rinsed  with  1  Quart  of  Water  at  150°  F. 


81 

15  900  000 

230  000 

7.6 

82 

110  500  000 

520  000 

17.1 

83 

69  000  000 

3  830  000 

126.0 

84 

300  000  000 

8  510  000 

279.9 

85 

605  200  000 

11  500  000 

378.3 

86 

3  000  000  000 

44  500  000 

1  463.8 

87 

24  600  000  000 

1  840  000  000 

60  526.3 

Cans  Rinsed  with  1^  Quarts  of  Water  at  150°  F. 


88 

16  162  000 

243  000 

8.0 

89 

15  055  000 

302  000 

9.9 

90 

17  460  000 

310  000 

10.2 

91 

19  522  000 

335  000 

11.0 

92 

16  650  000 

401  000 

13.2 

93 

21  543  000 

417  000 

13-.  7 

94 

9  120  000 

470  000 

15.5 

95 

17  812  000 

475  000 

15.6 

96 

18  195  000 

490  000 

16.0 

97 

19  980  000 

502  000 

16.5 

98 

10  850  000 

810  000 

26.6 

99 

15  532  000 

1  295  000 

42.6 

100 

207  000  000 

6  500  000 

213.8 

101 

450  000  000 

28  010  000 

921.4 

102 

1  050  000  000 

37  507  000 

1  235.1 

103 

9  975  000  000 

265  000  000 

8  717.1 

148 


BULLETIN  No.  230 


[November, 


TABLE   3. — Continued.     EFFECT  OF  VARYING   AMOUNTS   AND   TEMPERATURES  OF 
RINSE  WATER  ON  GERM  LIFE  IN  CANS 


Number  of  germs 
removed  by  rinse 
water 


Number  of  germs 

remaining  in  can 

after  rinsing 


Germs  per  cc.  of 
milk  due  to  can 


Cans  Rinsed  with  2  Quarts  of  Water  at  150°  F. 


104 

800  000 

40  000 

1.3 

105 

1  200  000 

80  000 

2.6 

106 

3  600  000 

100  000 

3.3 

107 

2  600  000 

100  000 

3.3 

108 

2  200  000 

120  000 

3.9 

109 

2  000  000 

140  000 

4.6 

110 

2  000  000 

150  000 

4.9 

111 

2  600  000 

210  000 

6.9 

112 

210  000 

6.9 

113 

1  000  000 

220  000 

7.2 

114 

3  800  000 

230  000 

7.6 

115 

3  000  000 

240  000 

7.9 

116 

1  200  000 

240  000 

7.9 

117 

4  500  000 

270  000 

8.9 

118 

2  400  000 

460  000 

15.1 

119 

1  400  000 

460  000 

15.1 

120 

4  600  000 

560  000 

18.4 

121 

5  800  000 

1  040  000 

34.2 

122 

5  000  000 

1  510  000 

49.7 

123 

12  600  000 

3  390  000 

111.5 

124 

5  400  000 

4  200  000 

138.2 

125 

10  800  000 

4  700  000 

154.6 

126 

19  800  000 

7  510  000 

247.0 

127 

77  600  000 

24  400  000 

802.6 

128 

56  200  000 

38  590  000 

1  269.4 

129 

347  600  000 

50  700  000 

1  667.8 

130 

1  976  000  000 

67  500  000 

2  220.4 

131 

200  000  000 

77  000  000 

2  532.9 

132 

163  400  000 

95  620  000 

3  145.4 

133 

2  166  000  000 

113  000  000 

3  717.1 

134 

151  800  000 

116  520  000 

3  832.9 

135 

964  800  000 

252  500  000 

8  305.9 

136 

683  400  000 

294  000  000 

9  671.1 

137 

2  000  000  000 

313  000  000 

10  296.5 

138 

2  800  000  000 

403  000  000 

13  256.6 

139 

1  734  400  000 

420  000  000 

13  815.8 

140 

1  332  000  000 

560  000  000 

18  421.5 

141 

2  800  000  000 

613  000  000 

20  164.5 

142 

1  580  000  000 

1  040  000  000 

34  210.5 

143 

4  460  000  000 

1  183  000  000 

38  914.5 

144 

22  000  000  000 

3  130  000  000 

102  960.5 

Cans  Rinsed  with  4  Quarts  of  Water  at  150°  F. 


145 

2  520  000 

30  000 

1.0 

146 

1  200  000 

70  000 

2.3 

147 

5  600  000 

70  000 

2.3 

148 

2  400  000 

90  000 

2.9 

149 

800  000 

110  000 

3.6 

150 

10  800  000 

120  000 

3.9 

151 

3  200  000 

120  000 

3.9 

152 

5  200  000 

170  000 

5.6 

153 

6  800  000 

490  000 

16.1 

1920]                   ELIMINATION  OP  GERMS  FROM  DAIRY  UTENSILS                        149 

TABLE  3.  —  Continued.    EFFECT  OF  VARYING  AMOUNTS  AND  TEMPERATURES  OF 
RINSE  WATER  ON  GERM  LIFE  IN  CANS 

No.  of 
can 

Number  of  germs 
removed  by  rinse 
water 

Number  of  germs 
remaining  in  can 
after  rinsing 

Germs  per  cc.  of 
milk  due  to  can 

Cans  Rinsed  with  4  Quarts  of  Water  at  150°  F.     (Cont'd.) 


154 

4  400  000 

520  000 

17.1 

155 

14  800  000 

540  000 

17.8 

156 

6  800  000 

1  100  000 

36.1 

157 

2  120  000 

1  260  000 

41.4 

158 

36  800  000 

3  440  000 

113.2 

159 

16  000  000 

4  250  000 

139.8 

160 

27  200  000 

4  950  000 

162.8 

161 

56  400  000 

8  320  000 

273.7 

162 

57  200  000 

13  000  000 

427.6 

163 

67  200  000 

13  400  000 

440.8 

164 

107  600  000 

15  000  000 

493.4 

165 

126  800  000 

22  920  000 

753.9 

166 

61  200  000 

23  300  000 

766.4 

167 

304  400  000 

36  250  000 

1  192.4 

168 

235  600  000 

58  000  000 

1  907.9 

169 

296  000  000 

80  300  000 

2  641.4 

170 

322  800  000 

103  000  000 

3  388.2 

171 

163  600  000 

114  860  000 

3  778.3 

172 

482  800  000 

123  400  000 

4  059.2 

173 

1  172  000  000 

164  500  000 

5  411.2 

174 

4  547  600  000 

243  200  000 

8  000.0 

175 

40  800  000  000 

366  000  000 

12  039.5 

176 

3  664  000  000 

440  000  000 

14  473.7 

177 

1  724  000  000 

526  000  000 

17  302.6 

178 

6  400  000  000 

673  000  000 

22  138.2 

179 

4  544  000  000 

700  000  000 

23  026.3 

180 

4  584  000  000 

790-000  000 

25  986.8 

181   ' 

8  880  000  000 

922  000  000 

30  328.9 

182 

10  564  000  000 

970  000  000 

31  907.9 

183 

10  000  000  000 

1  385  000  000   - 

45  559.2 

Cans  Rinsed  with  1  Quart  of  Water  at  200°-208°  F. 


184 

2  400  000 

150  000 

4.9 

185 

1  000  000 

190  000 

6.2 

186 

3  700  000 

190  000 

6.2 

187 

1  300  000 

200  000 

6.6 

188 

1  700  000 

460  000 

15.1 

189 

7  300  000 

550  000 

18.1 

190 
191 

3  900  000 
5  300  OdO 

1  100  000 
1  700  000 

36.2 
55.9 

192 

6  900  000 

2  000  000 

65.8 

193 

14  500  000 

2  010  000 

66.1 

194 

6  100  000 

2  260  000 

74.3 

195 

5  000  000 

2  310  000 

75.9 

196 

9  300  000 

2  600  000 

85.5 

197 

11  400  000 

2  710  000 

89.1 

198 

3  900  000 

3  010  000 

99.0 

199 

4  400  000 

3  200  000 

105.3 

200 

72  400  000 

5  900  000 

194.1 

201 

25  400  000 

6  600  000 

217.1 

202 

60  000  000 

9  400  000 

309.2 

203 

71  600  000 

11  000  000 

361.8 

204 

370  000  000 

20  000  000 

657.9 

205 

140  000  000 

20  000  000 

657.9 

150 


BULLETIN  No.  230 


[November, 


TABLE 


3. — Continued.    EFFECT  OF  VARYING  AMOUNTS   AND  TEMPERATURES  OF 
RINSE  WATER  ON  GERM  LIFE  IN  CANS 


No.  of 
can 


Number  of  germs 
removed  by  rinse 
water 


Number  of  germs 

remaining  in  can 

after  rinsing 


Germs  per  cc.  of 
milk  due  to  can 


Cans  Rinsed  with  1  Quart  of  Water  at  200°-208°  F.     (Cont'd.) 


206 

37  000  000 

21  000  000 

690.8 

207 

24  800  000 

22  000  000 

723.7 

208 

20  300  000 

24  000  000 

789.5 

209 

34  400  000 

32  000  000 

1  052.6 

210 

44  900  000 

44  000  000 

1  447.3 

211 

95  600  000 

47  660  000 

1  567.8 

212 

234  300  000 

56  000  000 

1  842.2 

213 

345  300  000 

67  300  000 

2  213.8 

214 

210  000  000 

76  000  000 

2  500.0 

215  i 

620  000  000 

83  000  000 

2  730.3 

216 

50  300  000 

100  000  000 

3  289.5 

217 

530  000  000 

110  000  000 

3  618.4 

218 

1  100  000  000 

120  000  000 

3  947.4 

219 

5  000  000  000 

730  000  000 

24  013.2 

220 

9  000  000  000 

1  060  000  000 

34  868.4 

Cans  Rinsed  with  1>£  Quarts  of  Water  at  200°-206°  F. 


221 

3  093  000 

222 

3  600  000 

30  000 

0.9 

223 

7  380  000 

65  000 

2.1 

224 

5  844  000 

70  000 

2.3 

225 

1  087  500 

78  000 

2.6 

226 

1  705  500 

100  000 

3.3 

227 

1  462  500 

111  000 

3.7 

228 

1  200  000 

136  000 

4.5 

229 

1  855  500 

144  000 

4.7 

230 

6  474  000 

145  000 

4.8 

231 

20  535  000 

165  000 

5.4 

232 

12  070  500 

180  000 

5.9 

233 

579  000 

231  000 

7.6 

234 

1  263  000 

284  000 

9.3 

235 

11  177  500 

377  000 

12.4 

236 

7  957  000 

445  000 

14.6 

237 

8  845  000 

520  000 

17.1 

238 

11  310  000 

541  000 

17.8 

239 

3  075  000 

560  000 

18.4 

240 

3  543  000 

653  000 

21.5 

241 

1  222  500 

762  000 

25.1 

242 

6  738  000 

932  000 

30.7 

243 

12  513  000 

1  127  000 

37.1 

244 

44  775  000 

1  465  000 

48.2 

245 

1Q  462  500 

1  815  000 

59.7 

246 

12  607  500 

2  276  000 

74.9 

247 

83  025  000 

3  347  000 

110.1 

248 

77  362  500 

4  357  000 

143.3 

249 

32  512  500 

4  975  000 

163.7 

250 

34  725  000 

6  640  000 

218.4 

251 

94  575  000 

18  300  000 

601.9 

252 

359  850  000 

22  632  000 

744.5 

253 

456  000  000 

49  000  000 

1  611.8 

254 

360  000  000 

64  150  000 

2  110.2 

255 

1  800  000  000 

129  000  000 

4  243.4 

256 

1  905  000  000 

348  000  000 

11  447.4 

1920} 


ELIMINATION  OP  GERMS  FROM  DAIRY  UTENSILS 


151 


TABLE  3. — Continued.     EFFECT  OF  VARYING  AMOUNTS   AND    TEMPERATURES  OF 
RINSE  WATER  ON  GERM  LIFE  IN  CANS 


No.  of 
can 

Number  of  germs 
removed  by  rinse 
water 

Number  of  germs 
remaining  in  can 
after  rinsing 

Germs  per  cc.  of 
milk  due  to  can 

Cans  Rinsed  with  2  Quarts  of  Water  at  200°-208°  F. 


257 

200  000 

258 

4  200  000 

259 

200  000 

10  000 

.3 

260 

400  000 

10  000 

.3 

261 

600  000 

10  000 

.3 

262 

400  000 

10  000 

.3 

263 

400  000 

20  000 

.7 

264 

400  000 

30  000 

1.0 

265 

600  000 

50  000 

1.6 

266 

200  000 

50  000 

1.6 

267 

1  000  000 

60  000 

2.0 

268 

400  000 

60  000 

2.0 

269 

200  000 

60  000 

2.0 

270 

200  000 

80  000 

2.« 

271 

400  000 

80  000 

2.6 

272 

.  200  000 

100  000 

3.3 

273 

200  000 

150  000 

5.0 

274 

600  000 

160  000 

5.3 

275 

200  000 

160  000 

5.3 

276 

200  000 

220  000 

7.2 

277 

600  000 

230  000 

7.6 

278 

600  000 

280  000 

9.2 

279 

200  000 

300  000 

9.9 

280 

600  000 

300  000 

9.9 

281 

1  200  000 

320  000 

10.5 

282 

2  000  000 

390  000 

12.8 

283 

3  400  000 

460  000 

15.1 

284 

800  000 

530  000 

17.4 

285 

1  200  000 

530  000 

17.4 

286 

800  000 

610  000 

20.1 

287 

960  000 

690  000 

22.9 

288 

1  000  000 

700  000 

23.0 

289 

1  800  000 

710  000 

23.4 

290 

600  000 

760  000 

25.0 

291 

400  000 

1  160  000 

38.2 

292 

6  400  000 

1  170  000 

38.5 

293 

1  000  000 

1  290  000 

42.4 

294 

4  000  000 

1  320  000 

43.4 

295 

200  000 

1  500  000 

49.3 

296 

5  400  000 

1  570  000 

51.6 

297 

8  800  000 

1  600  000 

52.6 

298 

2  800  000 

1  710  000 

56.2 

299 

2  000  000 

2  300  000 

75.7 

300 

34  200  000 

2  320  000 

76.3 

301 

22  800  000  . 

2  710  000 

89.1 

302 

3  800  000 

2  850  000 

93.7 

303 

25  200  000 

2  900  000 

95.4 

304 

11  600  000 

3  420  000 

112.5 

305 

60  000  000 

3  620  000 

119.1 

306 

144  000  000 

5  300  000 

174.3 

307 

23  200  000 

10  780  000 

354.6 

308 

80  000  000 

11  200  000 

368.4 

309 

77  000  000 

15  920  000 

523.7 

152 


BULLETIN  No.  230 


[November, 


TABLE   3. — Continued.     EFFECT  OF  VARYING   AMOUNTS  AND  TEMPERATURES   OF 
RINSE  WATER  ON  GERM  LIFE  IN  CANS 


No.  of 
can 

Number  of  germs 
removed  by  rinse 
water 

Number  of  germs 
remaining  in  can 
after  rinsing 

Germs  per  cc.  of 
milk  due  to  can 

Cans  Rinsed  with  3  Quarts  of  Water  at  204°-208°  F. 


310 

210  000 

46  000 

1.5 

311 

381  000 

74  000 

2.4 

312 

960  000 

101  000 

3.3 

313 

306  000 

215  000 

7.1 

314 

7  260  000 

275  000 

9.0 

315 

2  955  000 

553  000 

18.2 

316 

2  676  000 

627  000 

20.6 

317 

2  106  000 

660  000 

21.7 

318 

6  231  000 

766  000 

25.2 

319 

7  371  000 

771  000 

25.4 

320 

9  900  000 

785  000 

25.8 

321 

15  636  000 

994  000 

32.7 

322 

5  496  000 

1  232  000 

40.5 

323 

17  106  000 

2  849  000 

93.7 

324 

69  750  000 

3  183  000 

104.7 

325 

2  040  000 

4  337  000 

142.7 

326 

444  750  000 

5  225  000 

171.9 

327 

243  000  000 

10  100  000 

332.2 

328 

118  800  000 

12  250  000 

403.0 

329 

777  000  000 

48  700  000 

1  602.0 

330 

1  387  500  000 

63  525  000 

2  089.6 

331 

1  014  000  000 

72  500  000 

2  384.9 

332 

997  500  000 

73  000  000 

2  401.3 

333 

5  880  000  000 

258  750  000 

8  511.5 

Cans  Rinsed  with  4  Quarts  of  Water  at  200°-208°  F. 


334 

10  000 

.3 

335 

30  000 

1  0 

336 
337 
338 
339 
340 
341 

1  200  000 
1  200  000 
1  200  000 
400  000 
800  000 

30  000 
30  000 
30  000 
40  000 
40  000 
50  000 

1.0 
1.0 
1.0 
1.3 
1.3 
1  6 

342 

60  000 

2.0 

343 
344 

2  800  000 

70  000 
80  000 

2.3 
2  6 

345 
346 
347 

1  200  000 
4  400  000 

80  000 
100  000 
120  000 

2.6 
3.3 
3.9 

348 
349 
350 

1  200  000 
7  600  000 

130  000 
340  000 
750  000 

4.4 
11.1 
24.7 

351 
352 
353 
354 

1  600  000 
2  000  000 
60  800  000 
6  000  000 

1  050  000 
1  060  000 
1  430  000 
1  600  000 

34.5 
34.9 
47.0 
52.6 

ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS 


153 


TABLE  3. — Continued.     EFFECT   OF   VARYING  AMOUNTS  AND   TEMPERATURES  OF 
RINSE  WATER  ON  GERM  LIFE  IN  CANS 


Cans  Rinsed  with  6  Quarts  of  Water  at  190°-208°  F. 


No.  of 
can 

Number  of  germs 
removed  by 
rinse  water 

No.  of 
can 

Number  of  germs 
removed  by 
rinse  water 

No.  of 
can 

Number  of  germs 
removed  by 
rinse  water 

355 

378 

36  000 

401 

294  000 

356 

379 

42  000 

402 

300  000 

357 

6  000 

380 

48  000 

403 

300  000 

358 

6  000 

381 

60  000 

404 

360  000 

359 

12  000 

382 

60  000 

405 

444  000 

360 

12  000 

383 

60  000 

406 

534  000 

361 

12  000 

384 

66  000 

407 

600  000 

362 

12  000 

385 

72  000 

408 

600  000 

363 

12  000 

386 

84  000 

409 

600  000 

364 

12  000 

387 

90  000 

410 

648  000 

365 

12  000 

388 

102  000 

411 

678  000 

366 

18  000 

389 

120  000 

412 

678  000 

367 

18  000 

390 

120  000 

413 

1  332  000 

368 

18  000 

391 

120  000 

414 

1  500  000 

369 

18  000 

392 

120  000 

415 

1  524  000 

370 

24  000 

393 

150  000 

416 

1  716  000 

371 

24  000 

394 

150  000 

417 

2  154  000 

372 

24  000 

395 

174  000 

418 

2  424  000 

373 

24  000 

396 

180  000 

419 

3  120  000 

374 

30  000 

397 

246  000 

420 

9  612  000 

375 

36  000 

398 

258  000 

421 

19  600  000 

376 

36  000 

399 

264  000 

377 

36  000 

400 

264  000 

No.  of 
can 

Number  of  germs 
removed  by  rinse 
water 

Number  of  germs 
remaining  in  cans 
after  rinsing 

Germs  per  cc.  of 
milk  due  to  can 

Four  Cans  Rinsed  in  Succession  by  Same  Lot  of  6  Quarts  of  Water  at  190°  F. 


422 

10  000 

3 

423 

25  000 

8 

424 

45  000 

1  5 

425 

85  000 

2  8 

426 

30  000 

1  0 

427 

50  000 

1  6 

428 

5  000 

2 

429 

105  000 

3.5 

Four  Cans  Rinsed  in  Succession  by  Same  Lot  of  6  Quarts  of  Water  at  205°  F. 


430 

20  000 

7 

431 

170  000 

5  6 

432 

200  000 

6  6 

433 

765  000 

25  2 

434 

55  000 

1  8 

435 

18  825  000 

619  2 

436 

200  000 

6.6 

437 

1  680  000 

55.3 

154 


BULLETIN  No.  230 


[November, 


TABLE  3. — Concluded.    EFFECT  OF  VARYING  AMOUNTS  AND  TEMPERATURES  OF 
,  RINSE  WATER  ON  GERM  LIFE  IN  CANS 


No.  of 
Can 


Number  of  germs 

removed  by  rinse 

water 


Number  of  germs 

remaining  in  cans 

after  rinsing 


Germs  per  cc.  of 
milk  due  to  can 


Four  Cans  Rinsed  in  Succession  by  Same  Lot  of  9  Quarts  of  Water  at  206°-208°  F. 


438 

1  233  000 

144  000 

4.7 

439 

1  593  000 

22  000 

.7 

440 

29  385  000 

2  892  000 

95.1 

441 

460  800  000 

35  000  000 

1  151.3 

442 

351  000 

50  000 

1.6 

443 

1  710  000 

2  750  000 

90.5 

444 

3  015  000 

24  750  000 

814.1 

445 

1  665  000  000 

107  000  000 

3  519.7 

446 

315  000 

280  000 

9.2 

447 

1  530  000  000 

31  500  000 

1  036.2 

448 

1  305  000  000 

4  655  000 

153.1 

449 

2  790  000  000 

132  500  000 

4  358.6 

TABLE  4. — AVERAGE  NUMBER  OF  BACTERIA  IN  CANS  AFTER  BEING  RINSED 


Number 
of 
cans 

Amount 
of  rinse 
water 
used 

Temper- 
ature of 
rinse 
water 

Average  num- 
ber of  germs 
removed  by 
rinse  water 

Average  germ 
content  of 
cans  after 
rinsing 

Germ  content 
per  cc.  of 
milk  due 
to  can 

qts. 

°F. 

per  can 

per  can 

5 

1 

70 

1  196  460  000 

39  357 

20 

1.5 

70 

2  399  142  450 

319  448  250 

10  508 

12 

3 

70 

2  663  914  583 

257  390  000 

8  467 

35 

6 

70 

1  470  773  314 

7 

1 

150 

4  100  086  000 

1  909  090  000 

8  971 

16 

1.5 

150 

742  492  560 

21  441  750 

705 

41 

2 

150 

1  111  987  802 

215  073  414 

7  075 

39 

4 

150 

2  546  354  870 

200  225  129 

6  586 

37 

1 

200-208 

491  200  000 

72  716  216 

2  392 

36 

1.5 

200-206 

150  400  736 

18  433  694 

606 

53 

2 

200-208 

10  184  151 

1  561  698 

51 

24 

3 

204-208 

458  872  250 

23  396  583 

770 

21 

4 

200-208 

4  400  000 

339  524 

11 

67 

6 

190-208 

780  686 

Bacteriological  Condition  of  Cans  Rinsed  with  Water  at  150°  F. 

Too  close  comparisons  of  the  results  with  different  amounts  of  rinse 
water  cannot  be  made  because  the  testing  of  the  effect  of  1.5  quarts 
was  done  in  June,  1915,  and  the  remaining  tests  were  made  in  April, 
1916.  Again  only  seven  cans  were  tested  after  being  rinsed  with  one 
quart  of  water  at  150°  F.  and  these  seven  cans  were  all  examined  on 
the  same  day. 


1920']  ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS  155 

Bearing  these  facts  in  mind  it  will  be  seen  from  Table  4  that 
rinsing  cans  with  water  at  150°  F.  leaves  them  in  somewhat  better 
condition  than  when  rinse  water  at  70°  F.  is  used. 

Bacteriological  Condition  of  Cans  Rinsed  with  Water  at  190° -208°  F. 

Rinsing  dairy  utensils  on  the  farm  is  commonly  referred  to  as  scald- 
ing them.  Accordingly  there  is  an  unusual  interest  connected  with 
the  results  from  the  use  of  boiling  water.  On  this  account  the  num- 
ber of  cans  in  each  of  these  high-temperature  groups  is  large  and  the 
range  in  amounts  of  rinse  water  tested  is  wider  than  in  the  case  of 
the  other  temperatures. 

The  results  from  the  two  groups  of  cans  rinsed  with  one  quart 
and  three  quarts  of  water,  seem  unduly  high  as  compared  with  those 
from  the  other  groups.  An  inspection  of  the  detailed  results  as  given 
in  Table  3  shows  that  66  percent  of  the  bacteria  found  in  the  37  cans 
rinsed  with  one  quart  of  water  came  from  two  of  the  cans.  Had  the 
remaining  35  cans  been  filled  with  milk  they  would  have  increased  the 
germ  content  of  the  milk  but  835  bacteria  per  cc.  Among  the  24  cans 
rinsed  with  three  quarts  of  water,  three  cans  contributed  70  percent 
of  the  germs.  The  remaining  21  cans  would  have  increased  the  germ 
content  of  milk  by  only  231  bacteria  per  cc. 

Considering  these  results  as  a  whole  it  is  seen  that  these  cans  were 
in  much  better  condition  than  those  rinsed  with  cooler  water. 
When  a  can  is  rinsed  with  more  than  one  quart  of  boiling  water,  it 
will  rarely  add  1,000  bacteria  per  cc.  when  filled  with  milk.  "When  the 
amount  of  rinse  water  becomes  large,  the  effect  of  the  can  on  the  milk 
would  usually  be  below  100  per  cc. 

In  considering  the  relation  of  these  results  to  farm  practice  it 
should  be  remembered  that  the  water  available  for  rinsing  at  the  farm 
is  frequently  not  fully  up  to  the  boiling  point  and  the  amount  avail- 
able rarely  permits  the  use  per  can  of  the  larger  amounts  tested  in 
these  studies. 

Mechanical  Removal  and  Destruction  of  Bacteria  by  Rinse  Water 

References  have  already  been  made  (page  142)  to  the  high  germ 
content  of  rinse  water  in  commercial  plants.  This  suggests  that  rinse 
water  mechanically  removes  from  the  cans  a  large  amount  of  germ 
life.  Again  the  fact  that  rinsing  with  a  liter  of  sterile  water  gives  a 
usable  measure  of  the  germ  life  in  the  cans  is  further  evidence  of  the 
ease  with  which  water  loosens  and  removes  germs. 

By  using  sterile  rinse  water  at  a  temperature  too  low  to  destroy 
the  germs,  and  determining  the  germ  content  of  the  rinse  water  as  it 
comes  from  the  can,  the  mechanical  removal  may  be  accurately  meas- 
ured. When  the  temperature  of  the  rinse  water  is  increased,  its  effi- 
ciency in  removing  germ  life  is  probably  also  increased.  However,  a 


156  BULLETIN  No.  230  [November, 

count  of  the  living  germs  in  the  rinse  water  as  it  comes  from  the  can 
under  such  conditions  gives,  not  the  total  number  of  germs  removed, 
but  rather  the  total  number  removed  less  the  number  which  at  the 
same  time  have  been  destroyed  by  the  heat  of  the  rinse  water. 

When  the  cans  were  rinsed  with  water  at  70°  F.,  no  killing  effect 
occurred ;  and  from  Table  4  it  is  seen  that  as  an  average  of  seventy- 
two  cans  this  rinse  water  mechanically  removed  more  than  2  billion 
living  germs  per  can. 

When  rinse  water  was  applied  at  150°  F.,  the  average  number  of 
living  germs  found  in  the  rinse  water  from  the  103  cans  was  slightly 
under  2  billion  per  can.  When  but  one  quart  of  rinse  water  was  ap- 
plied, it  was  promptly  cooled  below  the  temperature  at  which  germs 
are  destroyed,  as  shown  in  Table  1.  The  average  number  of  living 
germs  found  in  the  rinse  water  from  7  cans,  each  rinsed  with  one 
quart  at  150°  F.,  was  practically  double  the  average  of  the  rinse  water 
at  70°  F.,  but  85  percent  of  these  germs  came  from  a  single  can.  The 
average  germ  content  of  the  rinse  water  from  the  other  six  cans  was 
683,433,333.  The  temperatures  given  in  Table  1  indicate  that  when 
larger  amounts  of  rinse  water  were  used  the  rinse  water  remained  for 
only  a  few  seconds  at  a  temperature  sufficiently  high  to  destroy  germ 
life.  Allowing  for  the  variation  noted  in  the  cans  rinsed  with  one 
quart  of  water  at  150°  F.,  the  measurements  of  germ  life  as  given  in 
Table  4  indicate  the  removal  of  an  increasing  number  of  bacteria  by 
the  use  of  increasing  amounts  of  rinse  water. 

The  small  number  of  living  germs  in  the  rinse  water  at  190°-208°  F. 
makes  it  quite  clear  that  here  the  effect  of  mechanical  removal  is  over- 
shadowed by  the  destructive  effect  of  the  high  temperature.  Even 
where  but  one  quart  was  applied  the  average  germ  content  of  the  rinse 
water  from  37  cans  was  only  one-half  billion  per  can  as  contrasted 
with  about  2  billion  per  can  where  cooler  water  was  applied.  With 
the  use  of  increasing  quantities,  the  water  remains  at  destructive  tem- 
peratures for  a  longer  time,  and  fewer  germs  survive  in  the  rinse 
water.  The  result  from  the  use  of  three  quarts  of  rinse  water  is  an  ap- 
parent exception,  but  an  inspection  of  the  detailed  results  in  Table  3 
shows  that  these  high  averages  were  due  to  the  results  from  a  few  cans. 

From  the  data  here  presented  it  would  appear  that  the  use  of  one 
quart  of  rinse  water  per  can,  at  a  temperature  of  150°  F,,  gives  good 
results  in  the  mechanical  removal  of  germ  life  but  has  only  a  small 
destructive  effect  upon  the  germs  present.  With  the  use  of  larger 
amounts  of  water  at  150°  F.,  or  the  same  amount  at  higher  tempera- 
tures, the  removal  or  destruction  of  germ  life  is  constantly  increased. 


1920]  ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS  157 


PART  II.     ELIMINATION  OF  GERMS  FROM  CANS  BY 
DRYING  IN  SUN  AND  AIR 

Between  May  22  and  June  9,  1917,  two  hundred  and  thirteen  cans 
and  fifty-eight  pails,  after  having  been  washed  and  rinsed  as  described 
on  page  141,  were  inverted  on  a  rack  and  exposed  to  sun  and  air. 
This  rack  was  located  on  the  south  side  of  a  farm  building  so  that 
the  utensils  might  have  the  fullest  exposure  to  the  sun.  It  should  be 
noted,  however,  that  their  inner  surfaces  were  not  exposed  to  the  di- 
rect rays  of  the  sun,  and  hence  the  data  in  this  study  have  no  rela- 
tion to  the  disinfecting  action  of  direct  sunlight.  Each  day  the  pails 
and  cans  were  placed  on  the  rack  at  8  a.  m.  At  4  p.  m.,  after  having 
been  exposed  for  eight  hours,  all  the  pails  and  half  of  the  cans  were 
examined.  The  remaining  half  of  the  cans  were  examined  at  4  a.  m. 
the  following  morning.  The  examination  consisted  first,  of  noting 
whether  the  utensils  were  dry,  clean,  and  free  from  odors,  and  second, 
of  determining  the  number  of  bacteria  in  each  according  to  the 
method  already  described  on  page  141. 

The  fourteen  check  cans  used  in  connection  with  these  experiments 
were  examined  for  bacteria  immediately  after  being  washed  and  rinsed. 

The  results  of  the  bacteriological  examinations  are  given  in  Table  5. 
The  number  of  bacteria  found  in  each  utensil  at  the  time  it  was  re- 
moved from  the  drying  rack  is  recorded,  and  the  numbers  so  obtained 
are  also  stated  in  terms  of  the  number  of  bacteria  which  would  have 
been  added  per  cc.  of  milk  had  each  utensil  been  filled  with  sterile  milk. 


As  far  as  could  be  judged  by  ordinary  inspection,  the  cans  and 
pails  which  had  been  inverted  on  the  rack  for  eight  and  twenty  hours 
respectively  were  in  good  condition  for  receiving  milk.  They  were 
uniformly  clean  and  free  from  any  odor. 

All  of  the  cans  held  for  eight  hours  appeared  dry  at  the  time  of 
final  examination  except  those  of  May  22.  On  this  day  rain  had  fallen 
fairly  continuously  and  the  humidity  had  evidently  prevented  drying. 
Similarly  moisture  was  evident  in  the  cans  held  for  twenty  hours,  on 
May  22  and  28,  rain  having  fallen  on  the  latter  night  as  well.  It 
rained  on  the  nights  of  May  23,  29,  31,  June  4,  and  5,  and  was  cloudy 
on  May  31  and  June  1.  No  moisture  was  found  in  these  cans  at  the 
close  of  the  twenty-hour  period  but  the  effect  of  the  weather  condi- 
tions upon  their  germ  content  is  discussed  on  page  164. 


158 


BULLETIN  No.  230 


[November, 


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ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS 


159 


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ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS 


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1920]  ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS  163 

NUMBER  OF  BACTERIA  IN  UNTREATED  CANS 

The  results  from  the  examinations  of  the  check  cans  were  quite  in 
accord  with  the  results  given  in  Bulletin  204  of  this  station  (pages 
222-239)  in  that  the  number  of  bacteria  present  in  apparently  similar 
cans  varied  to  an  astonishing  degree.  It  is  not  uncommon  to  find  a 
can  which  has  twenty  times  more  bacteria  than  other  cans  which  have 
had  apparently  identical  treatment.  Accordingly  the  number  of  bac- 
teria found  in  the  untreated  cans  is  only  a  rough  measure  of  the 
bacteria  that  may  have  been  present  in  the  treated  cans  before  they 
were  exposed  to  the  sun  and  air. 

Of  the  fourteen  check  cans,  eight  had  more  than  one  hundred  mil- 
lion bacteria  each,  and  the  smallest  number  was  7,100,000  bacteria. 
The  average  for  the  fourteen  cans  was  133,314,111  bacteria.  If  these 
cans  had  been  filled  with  milk  at  the  time  they  were  examined  they 
would  have  added  to  it  an  average  of  4,385  bacteria  per  cc.  of  milk. 

In  connection  with  other  studies  on  utensils,  several  hundred  in- 
dividual utensils,  mostly  cans,  have  been  examined.  All  the  utensils 
were  washed  in  a  similar  manner  and  by  the  same  operator  as  those 
used  in  these  studies,  so  that  they  may  be  taken  to  represent  in  a 
measure  the  condition  of  the  utensils  in  the  present  study  before  they 
were  placed  on  the  rack.  The  number  of  bacteria  found  in  the  cans 
first  referred  to,  which  were  examined  soon  after  they  were  washed, 
was  invariably  much  larger  than  the  number  found  in  the  check  cans 
in  this  study:  for  example,  a  set  of  fifty  cans  would  have  added 
87,059  bacteria  per  cc.  of  milk;  and  another  set  of  thirty-two  cans 
would  have  added  47,863  bacteria  per  cc.  of  milk  (Bulletin  204,  pages 
222-224). 

All  of  these  examinations  point  to  the  conclusion  that  the  cans 
selected  as  checks  in  this  study  contained  much  smaller  numbers  of 
bacteria  than  the  average  freshly  washed  can.  Accordingly  this  treat- 
ment of  the  utensils, — namely,  to  invert  them  on  the  rack  so  that  they 
are  exposed  to  the  air  and  the  sun, — undoubtedly  brings  about  a  more 
decided  reduction  in  the  germ  life  in  the  utensils  than  is  indicated 
by  comparison  with  the  numbers  found  in  these  check  cans. 

BACTERIA  IN  CANS  AND  PAILS  AFTER  EIGHT  HOURS  OF  EXPOSURE  TO 

SUN  AND  AIR 

The  number  of  bacteria  in  the  cans  and  pails  after  they  had  been 
exposed  to  sun  and  air  from  8  a.  m.  to  4  p.  m.  varied  widely.  The 
smallest  number  found  in  a  can  was  10,000  and  the  largest  was 
103,000,000.  Seventeen  percent  of  the  cans  and  10  percent  of  the 
pails  had  less  than  100,000  bacteria;  19  percent  of  the  cans  and 
14  per  cent  of  the  pails  had  more  than  100,000  and  less  than  one  mil- 
lion bacteria ;  and  64  percent  of  the  cans  and  76  percent  of  the  pails 
had  more  than  one  million  bacteria.  The  average  for  all  the  cans  was 
about  24,000,000  and  for  the  pails  about  10,000,000  bacteria. 


164  BULLETIN  No.  230  [November, 

The  importance  of  these  cans  and  pails  in  milk  contamination  may 
be  shown  by  calculating  how  many  bacteria  they  would  have  added 
to  the  milk  poured  into  them.  Such  calculation  shows  that  26  percent 
of  the  cans  and  14  percent  of  the  pails  would  have  added  less  than 
10  bacteria  per  cc.  of  milk ;  25  percent  of  the  cans  and  15  percent  of 
the  pails  would  have  added  more  than  10  and  less  than  100  bacteria; 
30  percent  of  the  cans  and  50  percent  of  the  pails  would  have  added 
more  than  100  but  less  than  1,000  bacteria ;  and  13  percent  of  the  cans 
and  21  percent  of  the  pails  would  have  added  more  than  1,000  bac- 
teria per  cc.  The  average  contamination  by  these  cans  would  have 
been  385  bacteria  per  cc.  of  milk  and  by  the  pails  848  bacteria.  These 
calculations  are  based  on  the  assumption  that  each  utensil  is  filled 
with  milk  but  once.  In  actual  operations  each  pail  is  commonly  used 
in  milking  several  cows,  and  thus  is  filled  a  number  of  times,  so  that 
the  number  of  bacteria  added  to  the  milk  by  the  pails  in  practice 
would  be  smaller  than  the  above  calculated  number. 

A  comparison  of  these  results  with  those  from  the  check  cans  shows 
that  there  were  eleven  times  as  many  germs  in  the  check  cans  as  in 
those  cans  which  were  kept  on  the  rack  for  eight  hours.  Assuming 
that  the  cans  which  were  exposed  to  the  sun  and  air  had  approxi- 
mately the  same  germ  life  before  they  were  placed  on  the  rack  as 
the  check  cans,  it  is  evident  that  a  decided  reduction  in  the  germ  life 
in  the  cans  was  brought  about  by  this  treatment. 

BACTERIA  IN  CANS  AFTER  TWENTY  HOURS'  EXPOSURE  TO  SUN  AND  AIR 

The  data  given  in  Table  5  show  that  in  the  cans  of  May  22,  28,  29, 
31,  and  June  1,  4,  5,  and  6  more  bacteria -were  found  after  twenty 
hours  than  in  the  corresponding  cans  after  being  held  for  eight  hours. 
It  is  of  significance  in  this  connection  that  rain  fell1  on  each  of  these 
nights  except  June  1  and  on  this  night  the  relative  humidity  was  80 
at  7  p.  m.,  with  the  practical  certainty  that  this  increased  as  the  tem- 
perature fell  during  the  night,  it  being  90  at  7  a.m.  the  following 
morning.  Under  such  meteorological  conditions  a  deposition  of  mois- 
ture on  the  surface  of  the  cans  would  readily  occur  and  thus  produce 
conditions  favorable  to  germ  growth.  During  the  nights  of  May  23, 
24,  25,  and  June  7  and  8,  when  there  was  no  rain  and  the  relative 
humidity  was  much  lower,  the  germ  content  of  the  cans  held  for  twenty 
hours,  as  compared  with  those  held  eight  hours,  remained  fairly  con- 
stant or  continued  to  decrease. 

Of  the  101  cans  kept  on  the  rack  from  8  a.  m.  to  4  a.  m.  the  fol- 
lowing morning,  19  percent  would  have  added  less  than  10  bacteria 
per  cc.  of  milk,  26  percent  more  than  10  and  less  than  100,  28  percent 
more  than  100  and  less  than  1,000,  and  27  percent  more  than  1,000. 

*Data  furnished  from  the  record  sheets  of  the  Local  Volunteer  Weather 
Observation  Station  thru  the  kindness  of  Prof.  J.  G.  Hosier. 


1920}  ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS  165 

The  average  contaminations  per  cc.  of  milk,  if  all  the  cans  had  been 
filled,  would  have  been  1,303  bacteria. 

BACTERIA  IN  DRY  CANS  AND  IN  MOIST  CANS 

While  the  observations  summarized  in  Table  5  were  made  upon 
cans  held  under  conditions  identical  with  those  to  which  cans  are 
exposed  in  practice,  it  was  somewhat  difficult  to  interpret  the  results 
because  the  humidity  of  the  air  varied  so  widely.  Likewise  the  amount 
of  germ  life  present  in  the  cans  before  treatment  could  not  be  sat- 
isfactorily determined. 

For  the  purpose  of  supplementing  this  data,  a  test  was  made  dur- 
ing January  and  February,  1919,  with  eight-gallon  cans  which  had 
been  so  thoroly  steamed  as  to  render  them  free  of  germ  life.  After 
they  were  cool  and  dry  there  was  added  to  each  can  10  cc.  of  wash 
water  or  rinse  water  which  was  taken  from  vats  in  which  milk  uten- 
sils had  just  been  cleaned  and  the  germ  content  of  which  had  been 
carefully  determined.  After  adding  this  liquid  to  the  cans  they  were 
covered  and  shaken  vigorously  to  distribute  the  material  over  the 
inner  surface.  This  volume  of  liquid  was  chosen  because  observation 
had  shown  that  about  this  quantity  of  liquid  usually  remains  in  well- 
drained  cans. 

Six  eight-gallon  cans  were  treated  in  this  way  on  each  of  eight 
days.  On  each  day,  immediately  after  the  liquid  had  been  thoroly 
distributed  in  the  cans,  the  covers  were  removed  from  three  cans, 
which  were  left  lying  on  their  side,  but  left  on  the  other  three  cans. 
The  cans  were  then  held  for  twenty-four  hours  in  a  room  with  a  tem- 
perature of  approximately  70°  F.  and  a  relatively  low  humidity,  ordi- 
narily between  40  and  60. 

The  bacterial  life  found  in  these  two  groups  of  cans  at  the  end  of 
twenty-four  hours,  determined  according  to  the  methods  described  on 
page  141,  is  recorded  in  Table  6.  To  facilitate  comparisons  of  the 
results,  the  cans  are  grouped  in  the  order  of  the  increasing  amount 
of  original  inoculation  added  to  the  cans. 

Perhaps  the  most  evident  point  in  the  data  in  Table  6  is  the  lack 
of  any  apparent  relationship  between  the  extent  of  the  original  in- 
oculation placed  in  the  cans  and  the  amount  of  germ  life  found  at 
the  end  of  twenty-four  hours.  This  is  equally  evident  in  the  cans 
from  which  the  covers  had  been  removed  and  in  those  on  which  the 
covers  had  been  left.  This  suggests  that  the  final  germ  content  of  cans 
held  for  a  period  of  twenty-four  hours  during  warm  weather  depends 
more  upon  the  conditions  under  which  the  cans  are  held  than  upon 
their  germ  content  at  the  close  of  the  washing  process. 

In  all  but  three  of  the  cans  from  which  the  covers  were  removed 
the  germ  life  fell  quite  sharply  during  the  twenty-four  hours.  On 
the  other  hand,  in  all  the  covered  cans  the  germ  life  increased,  the 
extent  of  the  increase  varying  from  20  to  3,000  fold. 


166 


BULLETIN  No.  230 


[November, 


Of  the  twenty-four  cans  from  which  the  covers  were  removed  six- 
teen, if  filled  with  milk,  would  have  added  to  each  cc.  a  germ  content 
of  between  10  and  100;  four  would  have  added  between  100  and 
1,000;  three  between  1,000  and  10,000;  and  one  can  21,381  per  cc. 

Of  the  twenty-four  cans  which  stood  with  their  covers  on  there 
were  none  which  would  have  added  a  germ  content  below  10,000  per 

TABLE  6. — CHANGES  IN  BACTERIAL  LIFE  IN  COVERED  AND  IN  UNCOVERED  CANS 

DURING  TWENTY -FOUR  HOURS 
10  cc.  of  rinse  water  added  to  each  can  at  beginning  of  period 


No. 

of 
can 

Cans  Not  Covered 

No. 

of 
can 

Cans  Covered 

Germs 
remaining 
in  can 

Germs  per 
cc.  of 
milk  due 
to  can 

Germs 
remaining 
in  can 

Germs  per 
cc.  of 
milk  due 
to  can 

Each  Can  Inoculated  with  12,300,000  Bacteria 


1 

400  000 

13.1 

4 

24  375  000  000 

801  809.2 

2 

500  000 

16.4 

5 

31  200  000  000 

1  026  315.8 

3 

85  000  000 

2  796.0 

6 

35  350  000  000 

1  162  829.0 

Each  Can  Inoculated  with  42,200,000  Bacteria 


7 
8 
9 

1 

9 
25 

800 

000 
000 
000 

0 
0 
59 

2 
8 
2 

10 
11 
12 

1  610  000  000 
1  700  000  000 
3  500  000  000 

52 
55 

115 

960.5 
921.0 
131.5 

Each  Can  Inoculated  with  43,900,000  Bacteria 

13 
14 
15 

1 
35 

81 

400 
300 
750 

000 
000 
000 

46 
1  161 
2  689 

0 
1 
1 

16 
17 

18 

2  600  000  000 
2  680  000  000 
2  700  000  000 

85 
.       88 
88 

526.3 
157.9 
815.7 

Each  Can  Inoculated  with  46,900,000  Bacteria 

19 
20 
21 

1 
4 
5 

150 

875 
050 

000 
000 
000 

37 
160 
166 

8 
3 
1 

22 
23 

24 

7  000  000  000 
9  300  000  000 
11  800  000  000 

230 
305 

388 

263.1 
921.0 
157.9 

Each  Can  Inoculated  with  55,600,000  Bacteria 

25 
26 
27 

400 
550 
900 

000 
000 
000 

13 
18 
29 

1 
0 
6 

28 
29 
30 

3  740  000  000 
4  920  000  000 
5  220  000  000 

123 
161 
171 

026.3 
842.1 
710.5 

Each  Can  Inoculated  with  76,500,000  Bacteria 

31 
32 
33 

1 
2 

500 
000 
000 

000 
000 
000 

16 
32 
05 

4 
8 
7 

34 
35 
36 

1  500  000  000 
2  300  000  000 
2  700  000  000 

49 
75 

88 

342.1 
657.9 
815.7 

Each  Can  Inoculated  with  82,000,000  Bacteria 

37 
38 
39 

1 

280 
405 
700 

000 
000 
000 

9 
13 
55 

2 
3 
9 

40 
41 

42 

3  350  000  000 
4  750  000  000 
7  150  000  000 

110 
156 
235 

197.3 
250.0 
197.3 

Each  Can  Inoculated  with  115,500.000  Bacteria 


43 

5  600  000 

184.2 

46 

2  200  000  000 

72  368.4 

44 

44  000  000 

1  447.3 

47 

2  350  000  000 

77  302.6 

45 

650  000  000 

21  381.5 

48 

4  400  000  000 

144  736.8 

ELIMINATION  OF  GERMS  FROM  DAIRY  UTENSILS  167 

cc.  of  milk;  seventeen  cans  would  have  added  a  germ  content  of  be- 
tween 10,000  and  100,000 ;  five  cans  a  germ  content  of  between  100,000 
and  1,000,000;  and  two  cans  a  germ  content  of  over  1,000,000  per  cc. 

These  results  may  be  summarized  by  saying  that  the  worst  of  the 
open  cans  showed  less  than  one-half  the  germ  content  of  the  best  of 
the  cans  which  were  covered.  Had  all  the  cans  been  filled  with  sterile 
milk,  that  in  the  covered  cans  would  have  had  an  average  germ  con- 
tent of  247,772  per  cc. ;  while  similar  milk  in  the  open  cans  would 
have  had  an  average  germ  content  of  1,284  per  cc.,  and  two-thirds  of 
these  germs  would  have  come  from  a  single  one  of  the  twenty-four 
open  cans. 

Since  the  six  cans  used  each  day  were  practically  identical  except 
in  the  matter  of  moisture  the  marked  differences  in  final  germ  con- 
tent may  be  attributed  to  differences  in  moisture.  In  the  closed  cans 
the  moisture  could  not  escape,  the  air  promptly  became  saturated,  and 
the  conditions  for  the  growth  of  bacteria  became  good  over  the  entire 
inner  surface  of  the  can.  The  amount  of  germ  life  present  in  these 
moist  cans  at  the  end  of  twenty-four  hours  seemed  to  depend  mainly 
upon  the  vigor  of  the  germs  present  and  upon  the  amount  and  char- 
acter of  food  available  to  them. 

In  the  open  cans  evaporation  began  at  once.  Ordinarily  the  cans 
became  apparently  dry  within  a  few  hours.  However,  in  a  few  cans, 
probably  because  of  the  uneven  distribution  of  the  moisture,  the 
drying  was  materially  retarded  and  at  least  a  few  drops  of  water 
remained  in  the  cans  at  the  end  of  twenty-four  hours.  For  example, 
when  Cans  13,  14,  and  15  were  tested  at  the  end  of  twenty-four  hours, 
Can  13  seemed  quite  dry,  while  moisture  was  evident  in  Cans  14  and 
15.  The  examination  of  these  cans  indicated  a  germ  content  in  Can  13 
of  46  per  cc.,  while  Cans  14  and  15  had  a  germ  content  of  1,161  and 
2,689  per  cc.  respectively.  Again,  the  day  on  which  Cans  43,  44,  and 
45  were  tested  was  damp  and  rainy,  and  at  the  end  of  twenty-four 
hours  moisture  was  evident  in  all  of  the  cans  but  was  most  pro- 
nounced in  No.  45.  The  germ  content  found  in  these  cans  was  184, 
1,447,  and  21,381  per  cc.  respectively. 

These  observations  of  the  presence  of  moisture  in  certain  cans 
account  for  all  the  comparatively  high  numbers  found  in  the  cans 
from  which  the  covers  had  been  removed,  except  in  the  case  of  Can  3. 
The  notes  do  not  show  that  any  moisture  was  present  at  the  end  of 
twenty-four  hours  in  this  can,  but  the  whole  trend  of  the  data  makes 
it  highly  probable  that  the  can,  for  some  reason,  dried  very  slowly. 

IMPORTANCE  OF  DRYNESS  IN  CONTROLLING  (TERM  LIFE  IN  UTENSILS 

The  main  fact  which  stands  out  distinctly  as  the  result  of  the 
studies  reported  in  Part  II  is  the  overshadowing  importance  of  dry- 
ness  as  a  means  of  reducing  and  keeping  down  germ  life  in  utensils. 


168  BULLETIN  No.  230 

Pails  and  cans  given  such  a  washing  as  is  practicable  even  on  the 
farm,  where  steam  is  not  available,  will  add  to  the  milk  later  put  into 
them  less  than  100  bacteria  per  cubic  centimeter,  provided  they  are 
promptly  and  thoroly  dried  and  kept  dry  until  used. 

"When  the  sun  is  hot  and  the  air  dry,  the  exposure  of  the  utensils, 
with  the  covers  off,  to  the  heat  of  the  sun  is  a  satisfactory  treatment. 
However,  when  the  weather  is  rainy,  exposure  to  the  damp  air  does 
not  lead  to  quick  and  thoro  drying  and  under  such  conditions  the 
germ  life  in  the  utensils  may  hold  its  own  or  even  increase  in  number. 

GENERAL  DISCUSSION 

From  information  kindly  furnished  by  milk  companies  in  various 
cities  it  is  evident  that  the  morning's  milk  as  it  reaches  their  bottling 
plants  or  shipping  stations  in  warm  weather  rarely  contains  less  than 
50,000  bacteria  per  cc.  and  occasionally  exceeds  1,000,000  per  cc.  It 
should  be  remembered  that  the  interval  between  milking  and  deliv- 
ery in  these  cases  is  so  short  that  little  growth  has  occurred.  Accord- 
ingly the  above  large  numbers  of  bacteria  indicate  the  amount  of  seed- 
ing to  which  the  milk  is  normally  exposed  under  present  conditions. 

The  studies  described  in  Bulletin  204  make  it  evident  that  the  seed- 
ing of  the  milk  under  normal  conditions  comes  principally  from  the 
utensils  in  which  the  milk  is  handled.  It  further  points  out  that 
among  the  utensils  coming  into  contact  with  the  milk  up  to  the  time 
of  its  delivery  to  the  milk  plant,  the  cans  are  ordinarily  the  principal 
source  of  the  bacteria  added  to  the  milk. 

The  present  publication  points  out  that  the  amount  of  germ  life 
in  milk  cans  in  warm  weather  twenty-four  hours  after  they  have  been 
fairly  well  washed  is  controlled  principally  by  the  moisture  which  re- 
mains in  the  washed  cans. 

Observations  made  upon  the  milk  cans  as  sent  out  by  a  consider- 
able number  of  the  leading  milk  companies  show  that  a  considerable 
proportion  of  these  cans  are  moist  as  returned  to  the  producers.  Ac- 
cordingly in  these  cans  the  conditions  are  favorable  for  the  develop- 
ment of  an  amount  of  germ  life  which  will  fully  account  for  the  seed- 
ing which  the  milk  ordinarily  receives  before  it  reaches  the  milk  plant. 

The  present  publication  further  points  out  that  when  these  high 
germ  content  cans  reach  the  farm  a  rinsing  with  liberal  amounts 
of  water  at  or  near  the  boiling  point  will  so  reduce  the  number  of 
germs  in  them  that  if  used  immediately  they  will  ordinarily  add  only 
about  100  bacteria  per  cc.  to  the  milk.  It  also  points  out  that  if  such 
of  these  cans  as  are  not  needed  immediately  are  promptly  and  thoroly 
dried  and  kept  dry,  the  germs  in  them  will  not  grow  but  will  con- 
tinue to  decrease,  and  the  cans  when  used  will  have  little  effect  upon 
the  germ  content  of  the  milk. 


UNIVERSITY  OF  ILLINOIS-URBANA 


